Vacuum insulated glass (VIG) unit including nano-composite pillars, and/or methods of making the same

ABSTRACT

Certain example embodiments of this invention relate to composite pillar arrangements for VIG units that include both harder and softer materials. The softer materials are located on the outside or extremities of the central, harder pillar material. In certain example embodiments, a high aspect ratio mineral lamellae is separated by an organic “glue” or polymer. When provided around a high strength pillar, the combination of the pillar and such a nano-composite structure may advantageously result in superior strength compared to a monolithic system, e.g., where significant wind loads, thermal stresses, and/or the like are encountered.

FIELD OF THE INVENTION

Certain example embodiments of this invention relate to pillars used invacuum insulated glass (VIG) units. More particularly, certain exampleembodiments of this invention relate to composite pillar arrangementsfor VIG units that include both harder and softer materials, with thelatter being located on the outside or extremities of the central pillarmaterial. In certain example embodiments, a high aspect ratio minerallamellae is separated by an organic “glue” or polymer that, whenprovided around a high strength pillar, advantageously may result insuperior strength compared to a monolithic system, e.g., wheresignificant wind loads, thermal stresses, and/or the like areencountered.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Vacuum IG units are known in the art. For example, see U.S. Pat. Nos.5,664,395, 5,657,607, and 5,902,652, the disclosures of which are allhereby incorporated herein by reference.

FIGS. 1-2 illustrate a conventional vacuum IG unit (vacuum IG unit orVIG unit). Vacuum IG unit 1 includes two spaced apart glass substrates 2and 3, which enclose an evacuated or low pressure space 6 therebetween.Glass sheets/substrates 2 and 3 are interconnected by peripheral or edgeseal of fused solder glass 4 and an array of support pillars or spacers5.

Pump out tube 8 is hermetically sealed by solder glass 9 to an apertureor hole 10 which passes from an, interior surface of glass sheet 2 tothe bottom of recess 11 in the exterior face of sheet 2. A vacuum isattached to pump out tube 8 so that the interior cavity betweensubstrates 2 and 3 can be evacuated to create a low pressure area orspace 6. After evacuation, tube 8 is melted to seal the vacuum. Recess11 retains sealed tube 8. Optionally, a chemical getter 12 may beincluded within recess 13.

Conventional vacuum IG units, with their fused solder glass peripheralseals 4, have been manufactured as follows. Glass frit in a solution(ultimately to form solder glass edge seal 4) is initially depositedaround the periphery of substrate 2. The other substrate 3 is broughtdown over top of substrate 2 so as to sandwich spacers 5 and the glassfrit/solution therebetween. The entire assembly including sheets 2, 3,the spacers, and the seal material is then heated to a temperature ofapproximately 500° C., at which point the glass frit melts, wets thesurfaces of the glass sheets 2, 3, and ultimately forms hermeticperipheral or edge seal 4. This approximately 500° C. temperature ismaintained for from about one to eight hours. After formation of theperipheral/edge seal 4 and the seal around tube 8, the assembly iscooled to room temperature. It is noted that column 2 of U.S. Pat. No.5,664,395 states that a conventional vacuum IG processing temperature isapproximately 500° C. for one hour. Inventors Lenzen, Turner and Collinsof the '395 patent have stated that “the edge seal process is currentlyquite slow; typically the temperature of the sample is increased at 200°C. per hour, and held for one hour at a constant value ranging from 430°C. and 530° C. depending on the solder glass composition.” Afterformation of edge seal 4, a vacuum is drawn via the tube to form lowpressure space 6.

Unfortunately, the aforesaid high temperatures and long heating times ofthe entire assembly utilized in the formulation of edge seal 4 areundesirable, especially when it is desired to use a heat strengthened ortempered glass substrate(s) 2, 3 in the vacuum IG unit. As shown inFIGS. 3-4, tempered glass loses temper strength upon exposure to hightemperatures as a function of heating time. Moreover, such highprocessing temperatures may adversely affect certain low-E coating(s)that may be applied to one or both of the glass substrates in certaininstances.

FIG. 3 is a graph illustrating how fully thermally tempered plate glassloses original temper upon exposure to different temperatures fordifferent periods of time, where the original center tension stress is3,200 MU per inch. The x-axis in FIG. 3 is exponentially representativeof time in hours (from 1 to 1,000 hours), while the y-axis is indicativeof the percentage of original temper strength remaining after heatexposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis inFIG. 4 extends from zero to one hour exponentially.

Seven different curves are illustrated in FIG. 3, each indicative of adifferent temperature exposure in degrees Fahrenheit (° F.). Thedifferent curves/lines are 400° F. (across the top of the FIG. 3 graph),500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottomcurve of the FIG. 3 graph). A temperature of 900° F. is equivalent toapproximately 482° C., which is within the range utilized for formingthe aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2.Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled byreference number 18. As shown, only 20% of the original temper strengthremains after one hour at this temperature (900° F. or 482° C.). Such asignificant loss (i.e., 80% loss) of temper strength is of courseundesirable.

In FIGS. 3-4, it is noted that much better temper strength remains in athermally tempered sheet when it is heated to a temperature of 800° F.(about 428° C.) for one hour as opposed to 900° F. for one hour. Such aglass sheet retains about 70% of its original temper strength after onehour at 800° F., which is significantly better than the less than 20%when at 900° F. for the same period of time.

Another advantage associated with not heating up the entire unit for toolong is that lower temperature pillar materials may then be used. Thismay or may not be desirable in some instances.

Even when non-tempered glass substrates are used, the high temperaturesapplied to the entire VIG assembly may soften the glass or introducestresses, and partial heating may introduce more stress. These stressesmay increase the likelihood of deformation of the glass and/or breakage.

Moreover, VIG units are subject to extremely large static and dynamicloading as well as thermally induced stresses both during itsmanufacturing (e.g., during pump down and thermal seal processing) andthroughout its service life (e.g., during wind-loads or mechanical andthermal shocks). The pillar spacers used to mechanically support the gapbetween the two substrates tend to indent the glass surfaces with whichthey in contact, thereby creating indented areas from which cracks maypropagate and hence weakening the glass structure. The glass region justabove the pillar is under compressive stress, whereas the peripheralregion of the pillar is under tensile stress. It has been found that itis in the tensile regime that annealed glass is at its weakest state,and it has been found that any surface and bulk flaws in the tensilestress field may develop into cracks that may propagate. The magnitudeof the tensile stress component increases with the inter-pillar spacing,and the likelihood of the cracks forming and ensuing catastrophicbreakage increases once the stress field is above the strength of theglass. The surface profile or contour of the pillar is related to thelikelihood of any kind of Hertzian or coin shaped cracks.

One way to mitigate the indentation crack issue (e.g., while still beingaggressive on pillar spacing) is to use glass that has been temperedsuch that the surface skin of the glass is in a highly compressivestress that tends to “wash out” the tensile stress components induced bysupporting pillars. Unfortunately, however the VIG process takes placeat high temperatures and involves a thermal cycle duration thatpotentially can de-temper the glass.

Thus, it will be appreciated that there is a need in art to find asolution to the problems of and associated with indentation cracking. Italso will be appreciated that there is a need in the art for improvedVIG units, and/or methods of making the same.

In certain example embodiments of this invention, a vacuum insulatedglass (VIG) unit is provided. First and second substantially parallel,spaced apart glass substrates define a gap therebetween. An edge seal isprovided around a periphery of the first and second substrates to forman hermetic seal. A plurality of pillars is provided between the firstand second substrates. A lamellar coating is provided around at least aportion of the pillars so as to impart closure stresses on the firstand/or second substrates proximate to the pillars to at least partiallyoffset tensile stresses also applied to the first and/or second glasssubstrates. The gap is provided at a pressure less than atmospheric.

In certain example embodiments of this invention, a vacuum insulatedglass (VIG) unit is provided. First and second substantially parallel,spaced apart glass substrates define a gap therebetween. An edge seal isprovided around a periphery of the first and second substrates to forman hermetic seal. A plurality of pillars is provided between the firstand second substrates. A high-aspect ratio lamellar coating is providedbetween said pillars and the first and/or second substrates so as to atleast partially offset tensile stresses applied to the first and/orsecond glass substrates. The gap is provided at a pressure less thanatmospheric.

In certain example embodiments of this invention, a method of making avacuum insulated glass (VIG) unit is provided. First and second glasssubstrates are provided. A plurality of pillars are provided on thefirst glass substrate. The first and second substrates are sealedtogether (e.g., using at least one edge seal) such that the first andsecond substrates are in substantially parallel, spaced apartorientation to one another and to define a gap therebetween. The gap isevacuated to a pressure less than atmospheric. A lamellar coating isprovided between the pillars and the first and/or second substrates soas to at least partially offset tensile stresses also applied to thefirst and/or second glass substrates.

In certain example embodiments of this invention, a VIG unit isprovided. First and second substantially parallel, spaced apart glasssubstrates define a gap therebetween. An edge seal is provided around aperiphery of the first and second substrates to form a seal. A pluralityof pillars is provided between the first and second substrates, witheach said pillar being at least partially laminated with a materialselected to impart closure stresses on the first and/or secondsubstrates proximate to the pillar to at least partially offset tensilestresses also applied to the first and/or second glass substrates. Thegap is provided at a pressure less than atmospheric.

The features, aspects, advantages, and example embodiments describedherein may be combined to realize yet further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is a prior art cross-sectional view of a conventional vacuum IGunit;

FIG. 2 is a prior art top plan view of the bottom substrate, edge seal,and spacers of the FIG. 1 vacuum IG unit taken along the section lineillustrated in FIG. 1;

FIG. 3 is a graph correlating time (hours) versus percent temperingstrength remaining, illustrating the loss of original temper strengthfor a thermally tempered sheet of glass after exposure to differenttemperatures for different periods of time;

FIG. 4 is a graph correlating time versus percent tempering strengthremaining similar to that of FIG. 3, except that a smaller time periodis provided on the x-axis;

FIG. 5 is a cross-sectional view of a VIG unit incorporating a soft,lamellar coating and a hard pillar in accordance with certain exampleembodiments;

FIG. 6 is an enlarged portion of the FIG. 5 example embodiment thatdemonstrates the stress-reducing features of certain exampleembodiments;

FIG. 7 is a schematic view supporting the example strength optimizationtechniques of certain example embodiments;

FIG. 8 is a simplified schematic view demonstrating how a mineral orinorganic lamellae may be bound in an organic matrix in accordance withcertain example embodiments;

FIG. 9 is a simplified view demonstrating how the arrangement in FIG. 8may be capable of withstanding both tensile and shear stresses inaccordance with certain example embodiments; and

FIG. 10 is a graph showing a normalized stiffness-compositionrelationship in accordance with certain example embodiments.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

It will be appreciated that from a structural perspective, it would beadvantageous to provide a VIG unit with a high stiffness and highdamping behavior when it is subjected to dynamic loading. Further, itwould be advantageous to provide the VIG unit with a high storagemodulus to dissipate the energy. High damping or loss factor (tan δ)expressed as the ratio of loss modulus to the storage modulus is alsodesirable when attempting to avoid catastrophic failure of the VIG unit.Certain example embodiments therefore incorporate high Tg materials(such as, for example, MoSi₂, graphite platelets, etc.) and/or heatresistant polymers (such as, for example, aramids, silicones, etc.) incomposite pillar arrangements. Alternatively, or in addition, certainexample embodiments may incorporate carbon nanotubes (CNTs) in compositepillar arrangements, where such CNTs may be oriented such that they aregenerally perpendicular or generally parallel to the top and/or bottombases of the pillars.

More particularly, certain example embodiments relate to a compositepillar arrangement that includes both hard and softer materials, withthe latter being located on the outside or extremities of the centralpillar material. In certain example embodiments, the pillar may beshaped substantially as spheres, cylinders, donuts, C-rings, or anyother suitable shape, and they may be of or include hard and highstrength ceramics encapsulated with a nano-composite coating of orincluding polymeric, ceramic, and/or metallic components arranged in alamellar structure. The latter provides toughness, ductility, andvisco-elastcity. CNTs that are generally perpendicular or generallyparallel to the top and/or bottom bases of the pillars also may be usedin certain example embodiments as they tend not to burn off at hightemperatures, and they me disposed on the pillars via a CNT inclusiveink, from a metal catalyst (e.g., out of a hot gas), etc. See, forexample, application Ser. Nos. 12/659,352; 12/659,353; and 12/659,354,the entire contents of which are hereby incorporated herein byreference.

Lamellar structures generally include fine, alternating layers ofmaterials in the form of lamellae. In certain example embodiments ofthis invention, in general, the nano-composite pillar coatings includebuilding blocks on the nanometer scale. In certain example embodiments,a high aspect ratio mineral lamellae is separated by an organic “glue”or polymer. This may result in certain cases in superior strengthcompared to a monolithic system in circumstances where significant windloads and thermal stresses are encountered. The lamellar structure isoriented substantially parallel to the sliding surface, resulting in ahigh bearing-load combined with low shear stress, in certain exampleembodiments. Applications in metal forming that involve plasticdeformation, for example, may utilize solid lubricants.

FIG. 5 is a cross-sectional view of a VIG unit incorporating a soft,lamellar coating and a hard pillar in accordance with certain exampleembodiments. FIG. 5 is similar to FIGS. 1 and 2, except that lamellarcoatings 15 are provided between the pillar 5 and the first and secondsubstrates 2 and 3. The lamellar coatings 15 may be applied to thesubstrates prior to the placement of the pillar 5 in certain exampleembodiments. For instance, the lamellar coatings 15 may be applied in apattern on the substrates 2 and 3, they may applied across substantiallythe entire surfaces of the substrates 2 and 3, etc. In certain exampleembodiments, however, the lamellar coatings 15 may be applied to thepillars 5 directly. The pillars 5 may be coated at their edges and ends,they may be only on their ends, they may be substantially entirelyencapsulated by the coating, etc. In any event, the lamellar coatings 15may be disposed (directly or indirectly) on the substrates 2 and 3and/or the pillars 5 by any suitable technique including, for example,dip, spin, spray, roll, gravure, or other suitable technique. In certainexample embodiments, the pillars may be sapphire pillars.

FIG. 6 is an enlarged portion of the FIG. 5 example embodiment thatdemonstrates the stress-reducing features of certain exampleembodiments. The large arrows proximate to the edges of the substrate 2or 3 represent the tension that the glass is under due to the pillars.In contrast, the triangular area 19 represents the closure stressapplied by the lamellar coatings 15. This closure stress, which also isa form of tensile stress, may be quantified as discussed in greaterdetail below and is denominated as σ. This closure stress may compensatefor or otherwise offset some or all of the tension that the glass isunder.

Examples of softer phase coating materials will now be provided. MoS₂,like graphite, has a hexagonal crystal structure that is easy to shear.MoS₂ lubrication performance often exceeds that of graphite and iseffective in vacuum, as well, whereas graphite is not necessarily aseffective. The temperature limitation of MoS₂ at about 400 degrees C. isrestricted by oxidation. The particle size and film thickness parametersmay be matched to the surface roughness of the substrate. Largeparticles may result in excessive wear by abrasion caused by impuritiesin the MoS₂, whereas small particles may result in acceleratedoxidation. These parameters may be balanced in embodiments where MoS₂ isused as a softer phase coating material. As alluded to above, graphitealso may be used as a softer phase coating material. CNTs also may beused, as indicated above.

Boron nitride (e.g., hexagonal boron nitride) is another example softerphase coating material that may be used in connection with certainexample embodiments. Boron nitride is a ceramic powder lubricant thathas been found that have a high temperature resistance of about 1200degrees C. in an oxidizing environment.

Polytetrafluoroethylene (PTFE), unlike the other solid lubricantsdiscussed herein, does not have a layered structure. Rather, themacro-molecules of PTFE slip easily along each other, similar tolamellar-structures. PTFE shows one of the smallest coefficients ofstatic and dynamic friction, e.g., down to 0.04, and operatingtemperatures of at least about 260 degrees C. are possible with PTFE.

Another example of the proposed softer phase is a composite that is madeof a nano-clay and a polymer based on aramid a polymer known to bethermally stable and extremely strong. An example material describedherein is somewhat similar to a product commercially available under thetradename Kevlar from Dupont. However, unlike Kevlar, certain exampleembodiments involve making a polymer coating that can be cast from asolvent. This technique allows for better processing capability, lendsitself to be able to receive additives, and also confers better controlon attributes such as optical transparency.

More particular, a category of simple phenyl substitutednon-heterocyclic diamines such as diamino-heterocycle bearing diaminessuch as diaminotetraphenylethylenes and diamino-triphenylamine may beused in certain example embodiments. Starting from aromatic diamines, aseries of aramids and aromatic polyimides are synthesized in reasonablyhigh viscosities using a low-temperature solution polycondensation and atwo-step poly-addition, followed by cyclodehydration at hightemperature. Polymers with high viscosities may be obtained by changingthe type of diamine used. The polyamides so formed were amorphous andreadily soluble in organic solvents, despite having high viscosities.The solvents used were N-methyl-2-pyrrolidone (NMP),N-Ndimethylacetamide (DMAc), and m-cresol.

Soluble aramids with high viscosity advantageously produced atransparent, highly flexible, and tough film upon casting from DMAc.Such coatings had high Tg, ranging form about 330-350 degrees C. Infact, the temperature at which there was a 10% weight loss was aboveabout 500 degrees C. in air.

In certain example embodiments, nano-clay additives may be used in apolymer overcoat. For instance, prior to casting of the aramid polymer,about 5-10 wt. % of nano-clay may be added to the polymer dissolved inDMAc. After sonication for about 30 minutes, a nano-composite is formed,containing organically-treated clay that separates into nanometer-sizedplatelets and disperses throughout the polymer matrix (e.g., in asubstantially even manner). The additive has a large aspect ratio thathelps set the composite's properties.

In certain example embodiments, the polymer film may be cast over abatch of pillars and cured to form a coating around pillar materialsmade of harder ceramics than the composite coating. Unlike otherfillers, clay particles at the nano-size scale possess uniquecharacteristics. For example, the nano-clay particles are in plateletform with thickness of just 1 nm and width of about 70-150 nm in certaininstances. In certain example embodiments, the platelet size may be 1-10nm thick and 35-300 nm in width, more preferably 1-5 nm thick and 60-200width. This high aspect ratio imparts and fosters anisotropiccharacteristics to films that embed these particles. Platelets of theseexample sizes may be said to be nanometer-sized. Although certainexample embodiments refer to “platelets,” it will be appreciated thatthe exact shape and/or orientation of such particles need notnecessarily be plate-shaped. Other, more spherical, oblong, and/or othershapes and/or orientations may be used in connection with embodiments ofthis invention.

The nano-clay particles may be viewed as an “inorganic polymer” phasecomparable in size to the polymeric macromolecular component. Thisenables the formation of hybrids with novel physico-chemical properties.Such nano-composites may, for example, be use to encapsulate metallic orceramic pillars. In place of, or in addition to the particularnano-clays described above, moissonite or any silica or mica basedplatelet material may be used. Also as indicated above, graphite, CNTs,and/or the like may be used together with or in place of a nano-clay.

The specific surface area in certain example implementations is of theorder of about 700-800 sq/g. Therefore, the loading of only a fewpercent by weight (e.g., 1-15%, more preferably 1-10%, and still morepreferably 2-8%) of nano-clay into a polymer matrix may drasticallyalter the properties because of the high interfacial interaction. Theoptical transparency of the coating film may remain substantiallyunaltered, as the nano-size particles are too fine to scatter thevisible light (e.g., d<<λ). In other words, the inclusion of a nano-clayand polymer composite coating may have substantially no effect onvisible transmission.

An example improvement may be imparted by the nano-clay to the coatingand eventually to the VIG pillar so as to help reduce the likelihood ofcrack formation and buffer dynamic loads. This improvement may be basedon, for example, the high interfacial area leading to strong adsorptionof the aramid polymer molecules which, in turn, anchors the segmentalmotion of the polymers; the high aspect ratio providing a rigid layerstructure; chemical inertness, unlike glass materials under high stress;the existence of interlayer gaps or galleries of from about, forexample, 1-5 mm into which intercalated species may be inserted; dynamicexpandability of the gallery by several times with movement ofmacromolecules; etc.

The stress state in composites may be multi-axial and non-uniform, evenfor a uni-axial loading because of the complex interaction between thefiber and matrix. Hence, care should be taken to study the dynamicbehavior of the nano-composites, including understanding the elastic andfracture properties as well as potential interactions betweenfiber-matrix interface.

VIG units may benefit from the incorporation of nano-composite materialsprovided to harder pillars. For instance, the incorporation of suchmaterials may provide for enhanced heat resistance. Nano-clay increasesthe dimensional stability and the heat distortion temperature or T10 ofthe films. There is a marked reduction in weight loss upon heating dueto the decrease in decomposition by-products. Another advantage is thatthe transparency of the pillars increases with the nano-clay. Anotheradvantage relates to the ability to match the expansion coefficientthrough the selection of the materials used in the nano-composite. Stillanother advantage relates to the environmental stability of the polymerduring exposure to UV. The ablative nature of the polymer related to UVexposure is substantially reduced through the incorporation ofnano-composites.

In certain example embodiments, strength optimization may be performedaccording to the following.

FIG. 7 is a schematic view supporting the example strength optimizationtechniques of certain example embodiments. FIG. 7 shows that crackformation affects the material specimen strength at the macro-scale andnot always at the nano-scale. Consider, for example, the followingformulas:

$\begin{matrix}{\frac{\sigma_{ml}}{\sigma_{th}} = \frac{\sqrt{\pi}E_{i}\Psi}{\sigma_{th}}} & \left( {1a} \right) \\{\Psi = \sqrt{\frac{\gamma}{E_{ml}t}}} & \left( {1b} \right)\end{matrix}$Note also that:

$\begin{matrix}{{{Lim}\frac{\sigma_{ml}}{\sigma_{th}}}->1} & {t->t_{cr}} & {\Psi->\Psi^{*}}\end{matrix}$Thus:

$\begin{matrix}{t_{cr} = {\pi\left\lbrack \frac{\gamma\; E_{i}}{\sigma_{th}^{2}} \right\rbrack}} & (2)\end{matrix}$

$\left\lbrack \frac{\gamma\; E_{i}}{\sigma_{th}^{2}} \right\rbrack$is the characteristic length scale.For the purposes of the FIG. 7 example graph and the example equationsabove, σ is tensile strength, E_(i) is Young's Modulus, τ is shearstrength, γ is surface energy, and t is thickness. This assumes that γ=1J/m2, E_(i)=100 GPa, σi=E_(i)/30, and t_(cr) is about 30 nm.

FIG. 8 is a simplified schematic view demonstrating how a mineral orinorganic lamellae 25 may be bound in an organic matrix 27 in accordancewith certain example embodiments, and FIG. 9 is a simplified viewdemonstrating how the arrangement in FIG. 8 may be capable ofwithstanding both tensile and shear stresses in accordance with certainexample embodiments. The mineral or inorganic lamellae 25 may be able tosustain large tensile stresses without fracturing. This may befacilitated by virtue of the organic or softer matrix 27, which helps totransfer the load between mineral crystals in the mineral or inorganiclamellae 25. The organic matrix itself, and/or the organicmatrix/mineral layer interface therefore may be able to sustain highshear stresses without failure. Example high shear and tension zones areshown in FIG. 9, as are the overall tensile stresses (as indicated, forexample, with the σ arrows).

In other words:

$\begin{matrix}{\sigma_{i} = {\rho \cdot \tau_{p}}} & (3) \\{\frac{L}{t} = \frac{\sigma_{th}}{\tau_{p}}} & (4)\end{matrix}$

FIG. 10 is a graph showing a normalized stiffness-compositionrelationship in accordance with certain example embodiments. The x-axisgoes from organic-rich to mineral-rich (phi), where 0<φ<1. The y-axisplots E/E_(m) where:

$\begin{matrix}{\frac{E_{m}}{E} = {\frac{4\left( {1 - \phi} \right)}{X_{p}^{2}\phi^{2}} + \frac{1}{\phi}}} & (5)\end{matrix}$for different Xp values. Xp, in turn, is calculated according to thefollowing equation:

$X_{p} = {\frac{G_{p}}{E_{m}} \cdot {\rho^{2}.}}$

Certain design parameters have been found to impact the above. Forinstance, it has been determined that at a critical thickness scale,theoretical strength rather than the Griffith criterion, controlsfracture strength, implying an insensitivity to pre-existing flaws. Andesirable aspect ration may be given by a ratio of tensile strength ofthe mineral layer (ML) and shear strength of the organic matrix. Theamount of allowable organic or softer content may be determined as aproduct of the aspect ratio and organic matrix shear to Young's moduliratio.

It will be appreciated that the matrix or overcoat described inconnection with certain example embodiments may be a polymer-based orpolymer-inclusive overcoat. However, in certain example embodiments,other material such as silicone and/or the like may be used as apotential overcoat or matrix to be loaded with nanometer-sizedplatelets. In general, materials having a Tg of at least about 200degrees C. will be acceptable, with Tg of at least about 250 degreesbeing preferable, and Tg of at least about 300 degrees being still morepreferable.

“Peripheral” and “edge” seals herein do not mean that the seals arelocated at the absolute periphery or edge of the unit, but instead meanthat the seal is at least partially located at or near (e.g., withinabout two inches) an edge of at least one substrate of the unit.Likewise, “edge” as used herein is not limited to the absolute edge of aglass substrate but also may include an area at or near (e.g., withinabout two-inches) of an absolute edge of the substrate(s). Also, it willbe appreciated that as used herein the term “VIG assembly” refers to anintermediate product prior to the VIG's edges being sealed andevacuation of the recess including, for example, two parallel-spacedapart substrates. Also, while a component may be said to be “on” or“supported” by one or more of the substrates herein, this does not meanthat the component must directly contact the substrate(s). In otherwords, the word “on” covers both directly and indirectly on, so that thecomponent may be considered “on” a substrate even if other material(e.g., a coating and/or thin film) is provided between the substrate andthe component.

It will be appreciated that the example embodiments described herein maybe used in connection with a variety of different VIG assembly and/orother units or components. For example, the substrates may be glasssubstrates, heat strengthened substrates, tempered substrates, etc.

The terms “heat treatment” and “heat treating” as used herein meanheating the article to a temperature sufficient to enabling thermaltempering, bending, and/or heat strengthening of the glass. Thisincludes, for example, heating an article to a temperature of at leastabout 580 or 600 degrees C. for a sufficient period to enable temperingand/or heat strengthening, more preferably at least about 600 degreesC., and sometimes to 625 degrees C. In some instances, the HT may be forat least about 4 or 5 minutes.

It is noted that the glass substrate(s) may be heat treated in certainexample embodiments so that the glass substrate(s) is/are either heatstrengthened or thermally tempered (e.g., at a temperature of at leastabout 580 degrees C., more preferably at least about 600 degrees C., andoften at least about 620 or 640 degrees C.).

Certain example embodiments may provide localized heating to and/or IRheating of the frits as disclosed in, for example, application Ser. Nos.12/000,663 and 12/000,791, the entire contents of each which are herebyincorporated herein by reference. This may be facilitated by designingthe frit of certain example embodiments to absorb infrared, e.g., in the800-2000 nm regions (or any sub-regions therein). This may beaccomplished, for example, by providing additives that will absorb thesewavelengths. These additives may be provided at various times including,for example, during the batch recipe of the frit and melted into theglass frit, added as powder to the base powdered frit, etc. In suchcases, the frit preferably will heat up and melt while having only asmall, if any, impact on the beads included in the mixture.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A vacuum insulated glass (VIG) unit, comprising:first and second substantially parallel, spaced apart glass substratesdefining a gap therebetween; an edge seal provided proximate a peripheryof the first and second substrates to form a seal; a plurality ofspacers provided between the first and second substrates, each saidspacer being at least partially laminated with a material comprisingcarbon nanotubes (CNTs) to impart closure stresses on the first and/orsecond substrates proximate to the spacer to at least partially offsettensile stresses also applied to the first and/or second glasssubstrates, wherein the gap is provided at a pressure less thanatmospheric.
 2. The VIG unit of claim 1, wherein the CNTs are providedon one or both bases of the spacers such that the CNTs are generallyperpendicular thereto.
 3. A vacuum insulated glass (VIG) window unitcomprising: first and second substantially parallel spaced apart glasssubstrates defining a gap therebetween; an edge seal provided proximatea periphery of the first and second substrates to form a seal; aplurality of spacers provided between the first and second substratesfor helping maintain the gap between the first and second substrates,each said spacer comprising a carbon nanotube (CNT); and wherein the gapbetween the first and second substrates is provided at a pressure lessthan atmospheric.
 4. The VIG window unit of claim 3, further comprisinga getter in communications with the gap.
 5. The VIG window unit of claim3, wherein said spacers are arranged in an array between the first andsecond substrates.
 6. The VIG window unit of claim 3, wherein at leastone of the glass substrates is tempered.